Spinneret for extruding self-crimping hollow fibers, self-crimping hollow fibers, and method for producing self-crimping hollow fibers

ABSTRACT

The invention relates to a spinneret for extruding self-crimping hollow fibers including at least one capillary. The at least one capillary has at least one segmented opening, which has at least two opening segments spaced apart from each other in the cross-section. A first opening segment of the at least two opening segments has a first opening-segment width and a second opening segment of the at least two opening segments has a second opening-segment width. The second opening-segment width is wider than the first opening-segment width.

BACKGROUND OF THE INVENTION

The invention relates to a spinneret for extruding hollow fibers, a self-crimping hollow fiber, and a method for producing self-crimping hollow fibers.

From the state of the art, self-crimping hollow fibers are known which are extruded by means of a spinneret. There are known spinnerets comprising capillaries, wherein each capillary comprises a C-shaped opening. From said C-shaped opening, a hollow fiber profile will be extruded. After exiting from the opening, the ends of the extruded C-shaped hollow-fiber profile will become bonded to each other in the form of a hollow-fiber wall portion by fusion and will form a hollow fiber having a hollow-fiber wall. After the drafting of the hollow fibers, these will become crimped three-dimensionally under the effect of the spin orientations that have been generated. Further, such self-crimping hollow fibers can be generated by additional introduction of two melt flows which again will result in spin orientations. These fibers have a distinctly higher crimping intensity but require systems engineering of a distinctly more complex type and, thus, higher investment.

SUMMARY OF THE INVENTION

It is an object of the invention to provide self-crimping hollow fibers, a spinneret for extrusion of self-crimping hollow fibers and a method for producing self-crimping hollow fibers wherein the crimping intensity of the produced hollow fibers is improved while there is used a single melt flow, and wherein the hollow fibers can be produced in a simple manner.

The invention provides, according to one embodiment, a spinneret, wherein the spinneret comprises at least one capillary having a segmented opening, which has at least two opening segments spaced apart from each other in cross-section, wherein a first opening segment of said at least two opening segments has a first opening-segment width and a second opening segment of said at least two opening segments has a second opening-segment width, the second opening-segment width being wider than the first opening-segment width.

Due to the different widths of the opening segments, melt flows of different magnitudes will flow through the capillaries, thus generating a hollow fiber having asymmetrically shaped hollow-fiber walls with different wall thicknesses and curvatures and with different spin orientations. The hollow fibers produced in this manner have a very high crimping intensity after drafting.

The opening-segment width of the second opening segment may be at least 10% and at least 20% wider than the opening-segment width of the first opening segment. After drafting, the hollow fibers produced by such a spinneret have particularly good crimping properties and, respectively, a particularly high crimping intensity.

The opening-segment width of the second opening segment may be 10% to 50% and in particular 20% to 40% wider than the opening-segment width of the first opening segment. Differences in the opening-segment width in these ranges have the advantage that there will be produced hollow fibers with particularly high crimping intensities.

The opening segments can be round in an arcuate shape but can also be oval or angled.

With particular advantage, the at least two opening segments can each have a substantially semicircular shape.

The respective opening segments can comprise two longitudinal sides and two transverse sides, wherein the distance between the transverse sides of the mutually adjacent opening segments is selected in such a manner that the hollow-fiber wall portions extruded from the opening segments will be fused to each other on the transverse sides after exiting from the opening segments.

The opening-segment width of the respective opening segments may be constant, i.e. it will remain the same.

It is also possible to provide segmented openings comprising at least three or at least four opening segments, wherein, in such a case, there are provided at least a first and a second opening segment which have different opening-segment widths.

In a hollow fiber comprising a hollow-fiber wall extruded by a spinneret, wherein the hollow-fiber wall in cross section comprises at least two hollow-fiber wall portions, it can be provided that a first one of said at least two hollow-fiber wall portions has a first wall thickness and a second one of said at least two hollow-fiber wall portions has a second wall thickness, the second wall thickness being larger than the first wall thickness.

Due to the spin orientations generated during the melt flow through the capillaries, a produced hollow fiber of the above type is a self-crimping hollow fiber.

The at least two hollow-fiber wall portions can each have a constant wall thickness across the respective hollow-fiber wall portion, i.e. they each have an unvarying wall thickness.

The first hollow-fiber wall portion can have a constant wall thickness. The second hollow-fiber wall portion can have a constant wall thickness.

The first hollow-fiber wall portion and the second hollow-fiber wall portion may be connected to each other by fusion. This means that the at least two hollow-fiber wall portions are respectively connected by fusion with the adjacent hollow-fiber wall portions.

The wall thickness of the second hollow-fiber wall portion can be by at least 10% and preferably at least 20% larger than the wall thickness of the first hollow-fiber wall portion.

The wall thickness of the second hollow-fiber wall portion can be by 10% to 50% and preferably by 20% to 40% larger than the wall thickness of the first hollow-fiber wall portion. With such wall thickness ratios, the hollow-fiber wall portions have particularly good crimping intensities.

The first hollow-fiber wall portion and the second hollow-fiber wall portion can be made of the same material. The hollow fiber can thus be a mono-component hollow fiber.

The first hollow-fiber wall portion and the second hollow-fiber wall portion can be made of different materials. The hollow fiber can thus also be a bi-component hollow fiber.

The hollow-fiber wall portions can be curved, wherein the second hollow-fiber wall portion can have a stronger curvature than the first hollow-fiber wall portion. A hollow fiber comprising two hollow-fiber wall portions may have a “D”-shaped cross section.

Also hollow fibers comprising three or at least four hollow-fiber wall portions can be provided. In such a cast, there can be provided at least a first and a second hollow-fiber wall portion that have different wall thicknesses.

According to the present invention, there can be provided a method for producing hollow fibers by a spinneret, comprising the following method steps:

-   -   extruding polymeric material from an opening, segmented in cross         section, of a capillary of a spinneret, the opening comprising         at least two opening segments having different opening-segment         widths,     -   wherein, from the at least two opening segments, at least two         hollow-fiber wall portions are extruded, wherein, from a         respective opening segment, respectively one hollow-fiber wall         portion is extruded,     -   fusing the extruded hollow-fiber wall portions to each other         after exit from the opening, while forming a hollow fiber having         a hollow-fiber wall which in cross section comprises at least         two hollow-fiber wall portions with different wall thicknesses.         The hollow-fiber wall portions are thus connected to each other         by self-fusion.

After the above fusion connection, the hollow fiber can be heated whereby the crimping intensity will be further enhanced by post-shrinkage. The smaller the individual crimping arcs are, the more intense the crimping intensity will be.

The fusion-connected hollow fiber can be cooled and drafted. The undrafted hollow fiber preferably is still straight while, after drawing or drafting, the hollow fibers will be crimped.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereunder, exemplary embodiments of the invention will be explained in greater detail with reference to the drawing.

In the drawing, the following is schematically shown:

FIG. 1 shows a device for producing spinning fibers,

FIG. 2 is a bottom view of a spinneret,

FIG. 3 shows a segmented opening of the capillary,

FIG. 4a is a cross-sectional view of a furnished hollow fiber,

FIG. 4b is a cross-sectional view of a hollow fiber,

FIGS. 5a-5d are comparative views illustrating crimping intensities of different hollow fibers.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a device for producing spinning fibers. In a container 8, polymeric material can be arranged. After drying in a drying device 6, the polymeric material can be molten in a melting device 4. In a spinneret 1, this molten material will be pressed through capillaries. By use of press and metering pumps, the melt will be pressed through the capillaries and be withdrawn in the form of filaments and respectively fibers. After exiting from the spinneret, the filaments will be cooled in a blow-out hopper, not shown, in the region 12 and then can be wound onto drums or placed in vessels at a constant speed. The filaments can then directly or later be drafted in drafting devices 12, 14. In the present case, the filaments are hollow fibers 2.

In FIG. 2, the spinneret 1 is shown in greater detail from below. The spinneret comprises a plurality of capillaries 18. The capillaries 18 are the nozzle holes. As shown in FIG. 2, the capillary 18 comprises at least one segmented opening 16. The segmented opening 16 comprises, when seen in cross section, at least two mutually spaced opening segments 20, 22. From FIG. 2, it is evident that the spinneret comprises a plurality of capillaries, each of them adapted to extrude hollow fibers from it. The respective capillaries are of identical design so that a plurality of identical hollow fibers can be extruded.

The segmented opening 16 of capillary 18 as shown in detail in FIG. 3 comprises mutually spaced opening segments 20, 22. The first opening segment 22 of the at least two opening segments 20, 22 has a first opening-segment width 32. The opening-segment width is preferably determined in the radial direction of opening 16. The second opening segment 20 of the at least two opening segments 20, 22 has a second opening-segment width 34. The second opening-segment width 34 is wider than the first opening-segment width 32. Preferably, the opening-segment width 34 of the second opening segment 20 is by at least 10%, preferably at least 20% wider than the opening-segment width 32 of the first opening segment 22.

With particular preference, the opening-segment width 34 of the second opening segment 20 is by 10% to 50%, preferably 20% to 40% wider than the opening-segment width 32 of the first opening segment 22.

As is the case in the illustrated exemplary embodiment, the opening segments 20, 22 may be of an arcuate shape. Further, the opening segments 20, 22 may be curved concentrically. Also, the opening segments 20, 22 may be curved concentrically around the center 24 of opening 16. Further, the opening segments 20, 22 may be designed in a semicircular shape.

The respective opening segments 20, 22 each comprise longitudinal sides 28 and transverse sides 30. Between the transverse sides 30, respective webs 26 are arranged.

In the method for producing self-crimping hollow fibers 2 by the spinneret 1, a polymeric material is extruded from the opening 16, segmented in cross section, of the capillary 18 of spinneret 1. From the opening segments 20, 22, there is extruded respectively one hollow-fiber wall portion 40, 42. Since the first opening segment 22 and the second opening segment 20 have different opening-segment widths 32, 34, also the hollow-fiber wall portions 40, 42 extruded from the respective opening segments 20, 22 will have different wall thicknesses. After exiting from the opening 16, the extruded hollow-fiber wall portions 40, 42 will fuse to each other, wherein those regions will fuse to each other which are arranged in the area of the transverse sides 30 of the opening segments 20, 22. The hollow-fiber wall portions 40, 42 will thus fuse to each other also in the area of their lateral sides, so that there will be formed a hollow fiber 2 having a hollow-fiber wall which, in cross section, comprises two hollow-fiber wall portions 40, 42 with different wall thicknesses.

The distance between the transverse sides 30 of the opening segments 20, 22 is selected so that the hollow-fiber wall portions 40, 42 after exiting from the opening can fuse to each other. The extruded hollow-fiber wall portions 40, 42 become connected to each other by fusion.

Shown in FIG. 4a is a macroscopic picture of cross sections of hollow fibers 2 according to the invention. FIG. 4b shows an enlarged representation of a cross section of a hollow fiber 2 according to the invention.

As can be seen in FIGS. 4a and 4b , the hollow fiber comprises a hollow-fiber wall 48. When viewed in cross section, said hollow-fiber wall 48 comprises at least two hollow-fiber wall portions 40, 42. In the illustrated exemplary embodiment, there is shown a hollow-fiber wall 48 comprising two hollow-fiber wall portions 40, 42. However, also more than two hollow-fiber wall portions can be provided.

The first hollow-fiber wall portion 40 has a first wall thickness 44, and the second hollow-fiber wall portion 42 has a second wall thickness 46. The second wall thickness 46 of the second hollow-fiber wall portion 42 is larger than the first wall thickness 42 of the first hollow-fiber wall portion.

Both the wall thickness 44 of the first hollow-fiber wall portion 40 and the second wall thickness 46 of the second hollow-fiber wall portion 42 are preferably constant and respectively unvarying.

The hollow-fiber wall 48 of the illustrated exemplary embodiment, consisting of two hollow-fiber wall portions 40, 42, preferably has a D-shaped cross section. The second hollow-fiber wall portion 42 which has the larger wall thickness 46 is curved more than the first hollow-fiber wall portion 40 having the smaller wall thickness 44. Thereby, a D-shaped hollow-fiber cross section is generated. This is of particular advantage for the self-crimping properties of the hollow fiber.

The first hollow-fiber wall portion 40 and the second hollow-fiber wall portion 42 are connected to each other by fusion. This is the precondition for the crimping intensity of the hollow fiber. The hollow fibers 2 produced by means of a spinning method will receive their crimping preferably after the drafting performed e.g. by the drafting devices 12, 14.

FIGS. 5a to 5d shown the hollow fibers after drafting. The fibers were glued onto black panels and compared to each other under the aspect of quality. Of relevance are only the crimped portions. The straight portions are undrafted fibers because the samples were drafted by hand.

In FIG. 5a , a hollow fiber is shown that was produced by a spinneret, wherein the capillary of the spinneret comprised a segmented opening with opening segments spaced apart from each other in cross section. The opening-segment widths of the respective opening segments were identical.

In FIG. 5b , a hollow fiber is shown that was produced under the same test conditions as the hollow fiber according to FIG. 5a , however, with the difference that a spinneret according to the invention was used whose capillaries comprised segmented openings having different opening-segment widths. The second opening-segment width of the second opening segment was by 20% wider than the opening-segment width of the first opening segment.

In FIG. 5c , a hollow fiber is shown that was produced under the same test conditions as the hollow fibers according to FIGS. 5a and 5b , however, with the difference that the segmented opening of the respective capillary comprises, in cross section, a first opening segment and a second opening segment wherein the opening-segment width of the second opening segment was by 40% wider than the opening-segment width of the first opening segment.

As clearly depicted in FIGS. 5b -5 c, the crimping intensities of the hollow fibers produced by spinnerets of the invention whose opening segments had different widths, are substantially stronger than the crimping intensity according to FIG. 5a , as evident from the numerous small crimping arcs.

Further, the hollow fiber according to FIG. 5c had a slightly higher crimping intensity than the hollow fiber according to FIG. 5b . The hollow fibers according to FIGS. 5b and 5c both comprised a respective hollow-fiber wall having at least two hollow-fiber wall portions wherein the wall thickness of the first hollow-fiber wall portion and the wall thickness of the second hollow-fiber wall portion were different from each other.

In the tests, it was found that, when the opening-segment width of the second opening segment was by at least 5% and preferably by at least 20% wider than the opening-segment width of the first opening segment, the crimping intensity was especially good.

Further, it was found that, when the opening-segment width of the second opening segment was by 5% to 50% and preferably by 20% to 40% wider than the opening-segment width of the first opening segment, the crimping intensity was advantageous.

Also, it was found that, when the wall thickness of the second hollow-fiber wall portion was by at least 5% and preferably by at least 20% larger than the wall thickness of the first hollow-fiber wall portion, the crimping intensity was again advantageous.

Further, it was found that, when the wall thickness of the second hollow-fiber wall portion was by 5% to 50% and preferably by 20% to 40% larger than the wall thickness of the first hollow-fiber wall portion, the hollow fibers had particularly good crimping intensities.

The present invention has the advantage that, even in case of mono-component hollow fibers, particularly good self-crimping properties were obtained.

Due to the different opening-segment widths of the opening segments, different melt quantities will flow from the opening segments, which, after exiting, will become bonded to each other at the respective ends of the hollow-fiber wall portions and form a hollow fiber. Such a hollow fiber preferably has a D-shaped cross section. Each of the hollow-fiber wall portions has a different spin orientation, which will lead to a different drafting and shrinking behavior. After drafting, this asymmetry will lead to a self-crimping of the fibers. The above mentioned ratios of opening-segment widths and the different ratios of wall thicknesses were of particular advantage.

Finally, in FIG. 5d , there is shown a C-shaped self-crimping hollow fiber under identical spinning conditions. While this C-shaped self-crimping hollow fiber of FIG. 5d has large and relatively flat crimping arcs, the hollow fibers according to FIGS. 5b and 5c having the small and high arcs are crimped much more intensely. This will result in a higher wad, which—conversely—in applications as filling fibers will allow for a reduced filling weight for a given volume and thus will reduce the costs. 

1. A spinneret for extruding self-crimping hollow fibers, comprising at least one capillary, wherein said at least one capillary has at least one segmented opening, which has at least two opening segments spaced apart from each other in cross-section, wherein a first opening segment of said at least two opening segments has a first opening-segment width and a second opening segment of said at least two opening segments has a second opening-segment width, the second opening-segment width being wider than the first opening-segment width.
 2. The spinneret according to claim 1, wherein the opening-segment width of the second opening segment is by at least 10%, preferably at least 20% wider than the opening-segment width of the first opening segment.
 3. The spinneret according to claim 1, wherein the opening-segment width of the second opening segment is by 10% to 50%, preferably 20% to 40% wider than the opening-segment width of the first opening segment.
 4. The spinneret according to claim 1, wherein that the opening segments have a curved shape.
 5. The spinneret according to claim 1, wherein the opening segments are concentrically curved.
 6. The spinneret according to claim 1, wherein the at least two opening segments each have a substantially semicircular shape.
 7. The spinneret according to claim 1, wherein the respective opening segments comprise two longitudinal sides and two transverse sides, wherein the distance between the transverse sides of the mutually adjacent opening segments is selected in such a manner that the hollow-fiber wall portions extruded from the opening segments are fused to each other on the transverse sides after exiting from the opening segments.
 8. A self-crimping hollow fiber comprising a hollow-fiber wall extruded by means of a spinneret, comprising a hollow-fiber wall, wherein the hollow-fiber wall in cross section comprises at least two hollow-fiber wall portions, wherein a first one of said at least two hollow-fiber wall portions has a first wall thickness and a second one of said at least two hollow-fiber wall portions has a second wall thickness, the second wall thickness being larger than the first wall thickness.
 9. The self-crimping hollow fiber according to claim 8, wherein the first hollow-fiber wall portion and the second hollow-fiber wall portion each have a constant wall thickness.
 10. The self-crimping hollow fiber according to claim 8, wherein the first hollow-fiber wall portion and the second hollow-fiber wall portion are connected to each other by fusion.
 11. The self-crimping hollow fiber according to claim 8, wherein the wall thickness of the second hollow-fiber wall portion is by at least 10% and preferably at least 20% larger than the wall thickness of the first hollow-fiber wall portion.
 12. The self-crimping hollow fiber according to claim 8, wherein the wall thickness of the second hollow-fiber wall portion is by 10% to 50% and preferably by 20% to 40% larger than the wall thickness of the first hollow-fiber wall portion.
 13. The self-crimping hollow fiber according to claim 8, wherein the hollow-fiber wall portions are curved, the second hollow-fiber wall portion having a stronger curvature than the first hollow-fiber wall portion.
 14. A method for producing self-crimping hollow fibers a spinneret, by extruding polymeric material from an opening, segmented in cross section, of a capillary of a spinneret, said opening comprising at least two opening segments having different opening-segment widths, wherein, from said at least two opening segments, at least two hollow-fiber wall portions are extruded, wherein, from a respective opening segment, respectively one hollow-fiber wall portion is extruded, fusing the extruded hollow-fiber wall portions to each other after exit from said opening, while forming a hollow fiber having a hollow-fiber wall which in cross section comprises at least two hollow-fiber wall portions with different wall thicknesses.
 15. The method according to claim 14, wherein after said fusion connection, the hollow fiber is heated. 